Polymeric materials that have the ability to swell may be useful in a variety of applications. The mechanism of swelling depends on molecular-level processes that occur that are dictated by physical and chemical properties of the materials (Escobedo et al., Phys. Report 318:85 (1999)).
Sol-gel synthesis is a relatively simple and versatile method to prepare organic/inorganic polymers with diverse morphologies and chemical compositions (Wright, Sol-Gel Materials: Chemistry and Applications, Gordon and Breach Science Publ., Amsterdam (2001)). In contrast to hydrophilic polymers prepared from biomaterials (Khalid et al., Eur. J. Pharm. Sci. 15:425 (2002); Elvira et al., Biomaterials 1955 (2002)), dried sol-gels (or zerogels) composed of polymerized alkoxysilanes generate a SiO2 matrix that is characterized as inelastic and not prone to extensive swelling in solvents when fully dried. The lack of swelling is likely due to considerable condensation reactions that occur during the gelation and drying processes that crosslink the polymeric sol-gel material (Brinker et al., Sol-Gel Science. The Physics and Chemistry of Sol-Gel Processing, Academic Press (San Diego), Chapter 9 (1990)). Due to the inherent chemical structure of sol-gel materials, there are few reports of sol-gels that are swellable. Some sol-gel compositions have been formulated using amine-bridged silane precursors that swell in response to changes in pH (Rao et al., J. Sol-Gel Sci. and Tech. 26:553 (2003)) or temperature (Rao et al., Adv. Mater. 13:274 (2001); Rao et al., Adv. Mater. 14:443 (2002)) to generate “smart” materials. These amine-bridged sol-gels are only capable of very limited swelling.
Although the physical rigidity of zerogels is often viewed as a positive characteristic of these materials, there are potential applications for sol-gels that swell upon exposure to chemical agents. If the swelling is selective towards a particular type or class of chemicals, such a response could be used to generate a chemical sensor or actuator. Swellable materials may also be useful as sorbents for chemical spills, remediation technologies, and recovery technologies if the amount of swelling is substantial and at least moderately selective.
The present invention is directed to overcoming these and other deficiencies in the art.